Leading-Edge Receptivity of Moderately Supersonic Boundary Layers to Free-Stream Disturbances

2021 ◽  
pp. 793-803
Author(s):  
Pierre Ricco ◽  
M. E. Goldstein
Keyword(s):  
Boundary Layers ◽  
Free Stream ◽  
Leading Edge

Boundary layer development after a separated region

1998 ◽  
Vol 374 ◽  
pp. 91-116 ◽  
Author(s):  
IAN P. CASTRO ◽  
ELEANORA EPIK
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Turbulence Models ◽  
Separated Flow ◽  
Leading Edge ◽  
Turbulence Structure ◽  
Outer Flow ◽  
Free Stream Turbulence ◽  
Layer Region

Measurements obtained in boundary layers developing downstream of the highly turbulent, separated flow generated at the leading edge of a blunt flat plate are presented. Two cases are considered: first, when there is only very low (wind tunnel) turbulence present in the free-stream flow and, second, when roughly isotropic, homogeneous turbulence is introduced. With conditions adjusted to ensure that the separated region was of the same length in both cases, the flow around reattachment was significantly different and subsequent differences in the development rate of the two boundary layers are identified. The paper complements, but is much more extensive than, the earlier presentation of some of the basic data (Castro & Epik 1996), confirming not only that the development process is very slow, but also that it is non-monotonic. Turbulence stress levels fall below those typical of zero-pressure-gradient boundary layers and, in many ways, the boundary layer has features similar to those found in standard boundary layers perturbed by free-stream turbulence. It is argued that, at least as far as the turbulence structure is concerned, the inner layer region develops no more quickly than does the outer flow and it is the latter which essentially determines the overall rate of development of the whole flow. Some numerical computations are used to assess the extent to which current turbulence models are adequate for such flows.

Boundary-Layer Transition and Separation Near the Leading Edge of a High-Speed Turbine Blade

1985 ◽  
Vol 107 (1) ◽  
pp. 127-134 ◽  
Author(s):  
H. P. Hodson
Keyword(s):  
Boundary Layers ◽  
Turbine Blade ◽  
High Speed ◽  
Free Stream ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Initial Development ◽  
Free Stream Turbulence ◽  
Hot Film

The state of the boundary layers near the leading edge of a high-speed turbine blade has been investigated, in cascade, using an array of surface-mounted, constant-temperature, hot-film anemometers. The measurements are interpreted with the aid of inviscid and viscous prediction codes. The effects of Reynolds number, compressibility, incidence, and free-stream turbulence are described. In all cases, the initial development of the boundary layers was extremely complex and, even at design conditions, separation and reattachment, transition and relaminarization were found to occur.

scholarly journals The Effect of Wake-Passing and Free-Stream Turbulence on Laminar Gas Turbine Blade Boundary Layers

1993 ◽  
Author(s):  
David Greenblatt
Keyword(s):  
Boundary Layers ◽  
Turbine Blade ◽  
Free Stream ◽  
Leading Edge ◽  
Computational Procedure ◽  
Realistic Model ◽  
Computationally Efficient ◽  
Mean Flow ◽  
Free Stream Turbulence ◽  
Wake Passing

A computational procedure has been developed which accounts for the combined time-mean effect of wake-passing and free-stream turbulence on laminar turbine blade boundary layers. The procedure has the advantage of being computationally efficient as well as providing a realistic model of the unsteady nature of the flow. The procedure yielded the parameter TuReD/σD/2 for characterizing the time-mean flow in the leading edge region and the parameter Γ≡2T~u2σx/γ for describing the flow downstream of the stagnation point. A provisional comparison with stagnation flow experimental data showed that the procedure may be more general than initially expected.

Leading-edge receptivity to free-stream disturbance waves for hypersonic flow over a parabola

2001 ◽  
Vol 441 ◽  
pp. 315-367 ◽  
Author(s):  
XIAOLIN ZHONG
Keyword(s):  
Boundary Layer ◽  
Hypersonic Flow ◽  
Boundary Layers ◽  
Free Stream ◽  
Stokes Equations ◽  
Leading Edge ◽  
Bow Shock ◽  
Navier Stokes ◽  
Hypersonic Boundary Layer ◽  
Disturbance Waves

The receptivity of hypersonic boundary layers to free-stream disturbances, which is the process of environmental disturbances initially entering the boundary layers and generating disturbance waves, is altered considerably by the presence of bow shocks in hypersonic flow fields. This paper presents a numerical simulation study of the generation of boundary layer disturbance waves due to free-stream waves, for a two-dimensional Mach 15 viscous flow over a parabola. Both steady and unsteady flow solutions of the receptivity problem are obtained by computing the full Navier–Stokes equations using a high-order-accurate shock-fitting finite difference scheme. The effects of bow-shock/free-stream-sound interactions on the receptivity process are accurately taken into account by treating the shock as a discontinuity surface, governed by the Rankine-Hugoniot relations. The results show that the disturbance waves generated and developed in the hypersonic boundary layer contain both first-, second-, and third-mode waves. A parametric study is carried out on the receptivity characteristics for different free-stream waves, frequencies, nose bluntness characterized by Strouhal numbers, Reynolds numbers, Mach numbers, and wall cooling. In this paper, the hypersonic boundary-layer receptivity is characterized by a receptivity parameter defined as the ratio of the maximum induced wave amplitude in the first-mode-dominated region to the amplitude of the free-stream forcing wave. It is found that the receptivity parameter decreases when the forcing frequency or nose bluntness increase. The results also show that the generation of boundary layer waves is mainly due to the interaction of the boundary layer with the acoustic wave field behind the bow shock, rather than interactions with the entropy and vorticity wave fields.

Experiments on transitional boundary layers with wake-induced unsteadiness

1991 ◽  
Vol 231 ◽  
pp. 229-256 ◽  
Author(s):  
X. Liu ◽  
W. Rodi
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Leading Edge ◽  
Clear Correlation ◽  
Hot Wire ◽  
Test Plate ◽  
Streamwise Location ◽  
Boundary Layer Development ◽  
Wake Passing

Hot-wire measurements were carried out in boundary layers developing along a flat plate over which wakes passed periodically. The wakes were generated by cylinders moving on a squirrel cage in front of the plate leading edge. The flow situation studied is an idealization of that occurring on turbomachinery blades where unsteady wakes are generated by the preceding row of blades. The influence of wake-passing frequency on the boundary-layer development and in particular on the transition processes was examined. The hot-wire signals were processed to yield ensemble-average values and the fluctuations could be separated into periodic and stochastic turbulent components. Hot-wire traces are reported as well as time variations of periodic and ensemble-averaged turbulent fluctuations and of the boundary-layer integral parameters, yielding a detailed picture of the flow development. The Reynolds number was relatively low so that in the limiting case of a boundary layer undisturbed by wakes this remained laminar over the full length of the test plate. When wakes passed over the plate, the boundary layer was found to be turbulent quite early underneath the free-stream disturbances due to the wakes, while it remained initially laminar underneath the undisturbed free-stream regions in between. The turbulent boundary-layer stripes underneath the disturbed free stream travel downstream and grow together so that the embedded laminar regions disappear and the boundary layer becomes fully turbulent. The streamwise location where this happens moves upstream with increasing wake-passing frequency, and a clear correlation could be determined in the experiments. The results are also reported in a mean Lagrangian frame by following fluid parcels underneath the disturbed and undisturbed free stream, respectively, as they travel downstream.

The Effect of Wake-Passing and Free-Stream Turbulence on Laminar Gas Turbine Blade Boundary Layers

1994 ◽  
Vol 116 (3) ◽  
pp. 384-391 ◽  
Author(s):  
D. Greenblatt
Keyword(s):  
Boundary Layers ◽  
Turbine Blade ◽  
Free Stream ◽  
Leading Edge ◽  
Computational Procedure ◽  
Realistic Model ◽  
Computationally Efficient ◽  
Mean Flow ◽  
Free Stream Turbulence ◽  
Wake Passing

A computational procedure has been developed that accounts for the combined time-mean effect of wake-passing and free-stream turbulence on laminar turbine blade boundary layers. The procedure has the advantage of being computationally efficient as well as providing a realistic model of the unsteady nature of the flow. The procedure yielded the parameter TuReD/σD/2 for characterizing the time-mean flow in the leading edge region and the parameter Γ (≡ 2T˜Tu2σx/γ) for describing the flow downstream of the stagnation point. A provisional comparison with stagnation flow experimental data showed that the procedure may be more general than initially expected.

Effect of Periodic Wake Passing on Film Effectiveness of Discrete Cooling Holes Around the Leading Edge of a Blunt Body

1997 ◽  
Vol 119 (2) ◽  
pp. 292-301 ◽  
Author(s):  
K. Funazaki ◽  
M. Yokota ◽  
S. Yamawaki
Keyword(s):  
Blunt Body ◽  
Free Stream ◽  
Turbine Blades ◽  
Density Ratio ◽  
Leading Edge ◽  
Test Model ◽  
Free Stream Turbulence ◽  
Aero Engine ◽  
Secondary Air ◽  
Wake Passing

Detailed studies are conducted on film effectiveness of discrete cooling holes around the leading edge of a blunt body that is subjected to periodically incoming wakes as well as free-stream turbulence with various levels of intensity. The cooling holes have a configuration similar to that of typical turbine blades except for the spanwise inclination angle. Secondary air is heated so that the temperature difference between the mainstream and secondary air is about 20 K. In this case, the air density ratio of the mainstream and secondary air becomes less than unity, therefore the flow condition encountered in an actual aero-engine cannot be simulated in terms of the density ratio. A spoke-wheel type wake generator is used in this study. In addition, three types of turbulence grids are used to elevate the free-stream turbulence intensity. We adopt three blowing ratios of the secondary air to the mainstream. For each of the blowing ratios, wall temperatures around the surface of the test model are measured by thermocouples situated inside the model. The temperature is visualized using liquid crystals in order to obtain qualitative information of film effectiveness distribution.

Effects of Embedded Vortices on Film-Cooled Turbulent Boundary Layers

1989 ◽  
Vol 111 (1) ◽  
pp. 71-77 ◽  
Author(s):  
P. M. Ligrani ◽  
A. Ortiz ◽  
S. L. Joseph ◽  
D. L. Evans
Keyword(s):  
Heat Transfer ◽  
Boundary Layers ◽  
Film Cooling ◽  
Free Stream ◽  
Flow Behavior ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Boundary Layers ◽  
Stream Velocity ◽  
Longitudinal Vortices

Heat transfer effects of longitudinal vortices embedded within film-cooled turbulent boundary layers on a flat plate were examined for free-stream velocities of 10 m/s and 15 m/s. A single row of film-cooling holes was employed with blowing ratios ranging from 0.47 to 0.98. Moderate-strength vortices were used with circulating-to-free stream velocity ratios of −0.95 to −1.10 cm. Spatially resolved heat transfer measurements from a constant heat flux surface show that film coolant is greatly disturbed and that local Stanton numbers are altered significantly by embedded longitudinal vortices. Near the downwash side of the vortex, heat transfer is augmented, vortex effects dominate flow behavior, and the protection from film cooling is minimized. Near the upwash side of the vortex, coolant is pushed to the side of the vortex, locally increasing the protection provided by film cooling. In addition, local heat transfer distributions change significantly as the spanwise location of the vortex is changed relative to film-cooling hole locations.

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